Liquid cooled internal combustion (IC) engines are typically cooled by circulating the cooling liquid, usually water, through water passages in the engine block adjacent to the cylinder and combustion chamber walls of the engine. The water may be cooled by a radiator, or in the case of marine engines, the water is drawn from a lake or sea and discharged overboard.
Internal combustion engines convert, at best, only about one third of the heat energy, released from burning the fuel, into useful power. Another third of the heat leaves the engine with the exhaust gases and the remaining third is absorbed by the mechanical parts of the engine. It is this last third that the engine cooling system must remove from the engine. If most of the heat absorbed by the mechanical parts of the engine is not removed, over heating and engine damage will result. Fluids are generally circulated through engine passages to absorb the heat from the mechanical components. Common fluids used to cool engines are air, water, oil and glycol.
While it is well known that the failure to remove heat from the mechanical components of the engine can result in damage, it is also true that over cooling the engine can be harmful. Piston rings, used to seal the combustion gases within the cylinder and combustion chamber, are not totally effective and some combustion gases leak past the piston rings into the crankcase of the engine. These gases contain water and by-products of combustion that can be quite corrosive to engine parts if allowed to condense in a cold crankcase. Modern engine oils have additives that are reasonably effective at controlling the corrosive effects of normal amounts of "blow-by", as the leakage past the rings is called, but these additives can be overwhelmed if the engine is not soon warmed enough during operation to eliminate most of the condensation of combustion products within the crankcase.
Maintaining the oil temperature of the lubricating oil of the engine near the normal boiling point of water, 212.degree. F., will assure that the engine temperature is high enough to prevent most of the undesirable condensation of water and combustion products within the crankcase and subsequent oil dilution. In normal engine operation, after the engine has warmed up, a crankcase ventilation system or "breather" removes the blow-by bases from the engine in vapor form. Temperatures below about 280.degree. F. will prevent thermal break down of the oil. Thus, a range of oil temperatures from about 190.degree. to 280.degree. F. is most suited to long term engine operation.
Most liquid cooled engines have the cooling liquid contained in a recirculating system which includes a liquid to air heat exchanger or radiator to remove heat from the cooling liquid after it has passed through the engine. A thermostat is usually placed in the recirculating cooling systems to maintain the coolant, and as a result the engine, at a suitable temperature to prevent blow-by condensation.
Some marine engines, outboard motors in particular, do not utilize radiators or similar heat exchangers in the cooling system. These engines rely, for cooling, upon water drawn from the lake or sea in which they operate.
When lake or sea water is used to cool an engine, an important limitation is that the temperature of the cooling water not be allowed to exceed 140.degree. F. if minerals dissolved in some waters are to be prevented from forming deposits within the cooling passages. This maximum water temperature is relatively low compared to the 180.degree.-190.degree. F. minimums normally maintained in modem sealed recirculating systems employing glycol and water coolant.
The invention addresses the problem of low coolant temperatures encountered in the marine environment by exposing the oil to a large area of the engine through which heat will flow into the oil, particularly during low and partial load operation. A novel liquid to liquid heat exchanger built into the engine extracts some of the heat from the oil but maintains an oil to water temperature difference which allows both oil and cooling water temperatures to remain within the desired ranges during normal operations.
Liquid to liquid heat exchangers have been employed on marine engines in applications to remove excess heat from the oil. These applications are external additions to engines used when the problem of excessive oil temperatures are encountered. An example can be found on the Mercruiser Class 1 Offshore racing engines manufactured by the Mercury Marine Division of Brunswick Corporation. The invention which is the subject of this disclosure differs from past applications in that it is primarily designed to maintain a minimum oil temperature, rather than limit a maximum temperature, and is built or cast into the internal configuration of the engine block rather than being an external accessory.